Magnetic Interaction between Surface Engineered Rare-earth Atomic Spins

TL;DR

This study uses ab initio calculations to explore the magnetic interactions of rare-earth Gd adatoms on an insulating surface, revealing geometry-dependent ferromagnetic or antiferromagnetic coupling mechanisms.

Contribution

It is the first to analyze rare-earth spin-coupled adatoms and the effects of geometry on their magnetic interactions using first-principles methods.

Findings

Exchange coupling is antiferromagnetic in linear geometry.

Exchange coupling is ferromagnetic in diagonal geometry.

Different exchange mechanisms (direct, superexchange, RKKY) contribute variably.

Abstract

We report the ab initio study of rare-earth adatoms (Gd) on an insulating surface. This surface is of interest because of previous studies by scanning tunneling microscopy showing spin excitations of transition metal adatoms. The present work is the first study of rare-earth spin-coupled adatoms, as well as the geometry effect of spin coupling, and the underlying mechanism of ferromagnetic coupling. The exchange coupling between Gd atoms on the surface is calculated to be antiferromagnetic in a linear geometry and ferromagnetic in a diagonal geometry, by considering their collinear spins and using the PBE+U exchange correlation. We also find the Gd dimers in these two geometries are similar to the nearest-neighbor (NN) and the next-NN Gd atoms in GdN bulk. We analyze how much direct exchange, superexchange, and RKKY interactions contribute to the exchange coupling for both geometries by additional first-principles calculations of related model systems.